Method of heating metallurgical products

ABSTRACT

The technical province of this invention is the heating in a furnace or kiln of metallurgical products principally. The invention relates to a heating method and means for imparting to mutually spaced products resting on the hearth of a kiln of this kind successive individual advancing motions, each consisting of alternating elemental motions, of which one at least is of length different from that of the others. The advantage of the invention resides primarily in the recovery of the heat accumulated in the hearth on the uncovered parts thereof and its transmission along successive zones to the undersurfaces of the products being treated, with dwelling times in the kiln and a degree of filling thereof enabling maximum efficiency to be obtained.

United States Patent Dessarts [15] 3,656,719 [451 Apr. 18, 1972 [5 METHOD OF HEATING- METALLURGICAL PRODUCTS [72] Inventor: Pierre Marie Louis Dessarts, Paris, France [73] Assignee: Societe Anonyme Heurtey, Paris, France [22] Filed: Aug. 17, 1970 [21] App1.No.: 64,261

[30] Foreign Application Priority Data Aug. 19, 1969 France ..6928327 [52] U.S. Cl. ..263/6 R [51] [58] Field of Search ..263/6, 6 A

[56] References Cited UNITED STATES PATENTS 2,583,968 l/l952 Rosseau ..263/6 3,398,939 8/1968 Morton 3,556,492 1/1971 Hirata et al. 3,567,197 3/1971 Knaak ..263/6 FOREIGN PATENTS OR APPLICATIONS 762,353 l/l934 France ..263/6 Primary Examiner-Charles J. Myhre Att0rney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT The technical province of this invention is the heating in a furnace or kiln of metallurgical products principally.

The invention relates to a heating method and means for imparting to mutually spaced products resting on the hearth of a kiln of this kind successive individual advancing motions, each consisting of alternating elemental motions, of which one at least is of length different from that of the others.

The advantage of the invention resides primarily in the recovery of the heat accumulated in the hearth on the uncovered parts thereof and its transmission along successive zones to the undersurfaces of the products being treated, with dwelling times in the kiln and a degree of filling thereof enabling maximum efficiency to be obtained.

3 Claims, 4 Drawing Figures PATENTEMPRWBW 3,656,719

METHOD OF HEATING METALLURGICAL PRODUCTS The technical province of this invention is the heat treatment, in a furnace or kiln, of products such as metallurgical products.

In tunnel kilns heated from the arch, through which the products to be treated are caused to travel, notably by means of walking-beams, said products rest on the hearth and are spaced from one another proportionately to their thickness.

Now, if it is desired to heat thick products like slabs while avoiding the complexity of tunnel kilns which heat both faces thereof, it is necessary to adopt kiln lengths permitting at least near-equalization of the temperature through the thickness of the products. Such sizes are not only troublesome and costly but also result in a kiln which becomes greatly oversized if the product to be treated is a difierent one and has a relatively small thickness.

While this drawback can be overcome by so determining the rate of advance of the products that their dwelling time in a short kiln is sufficiently long, this obviously greatly reduces the output rate.

The present invention has for its object to overcome these disadvantages by providing a method of heating, in a furnace or a kiln, such products as metallurgical products, in ac cordance with which method different mutually spaced products, in a tunnel kiln imparting successive motions of advance thereto, have imparted to them alternating elemental motions the amplitudes of which are substantially equal to different multiples of the spacing between the products, at least one of the phases of motion having an amplitude greater than that of the others.

In this way, different expanses of the undersurfaces of the products undergoing treatment are caused to rest on hearth locations previously exposed to the radiation from the arch, whereby to absorb the heat accumulated thereat, each such resting of the product being accompanied by a partial heating of the undersurface, while the upper surface of each product is continuously exposed to the arch heat.

For heating thick products like slabs, if the interval between the products, which is substantially equal to their thickness, is approximately equal to one-third of their width, the motion will be composed of a first movement equal to said spacing, of a second movement of identical extent in the opposite direction, and of a third movement in the same direction as the first movement but equal to twice the amplitude thereof, whereby areas on the undersurface of each slab, of width equal to said mutual spacing, are fetched successively into contact with hearth areas of corresponding width that have been previously exposed to the arch heat, the whole being accomplished in three phases or elemental movements for each unit forward advance.

It should be noted that recourse has already been had to furnaces in which the treated product could be moved in two directions in unequal steps, but the object sought in such installations was entirely different and consisted primarily in permitting a rapid drawing of the furnace charge through a charging door if necessary.

In a kiln according to this invention it is preferable to use a hearth material which is at once an accumulator and good conductorof heat, whereby to offer a heat transfer coefficient favourable to rapid acquisition and returning of the accumulated heat.

Better still, a hearth of this kind may comprise not only the accumulating layer but also a subjacent insulating layer.

In the case of a walking-beam furnace, the elemental movements and ultimately the unit forward advances can be obtained by any convenient electric control means or unit providing mechanical motions by means of combinations of earns, a Geneva mechanism, and like arrangements.

By way of an additional advantage, it is to be noted that the surface of the hearth is constantly maintained at temperature levels close to that reached by the metal being treated, thus ensuring satisfactory behaviour of the hearth with time and thereby accordingly providing a system having in-built protection against possible meltings of the oxides entering into the composition of the hearth material. In this way it is possible to operate at higher heat-emission temperatures.

For while the hearth surface temperature is directly dependent on said heat-emission temperature, on the other hand because of the heat absorptions by the product being treated consecutively at all points on the hearth, the health surface temperature remains lower than what it would be if no such absorption took place and consequently lies below the permissible limit.

The aforementioned various dispositions result in a more economical kiln design permitting more flexible operation and resulting in considerably improved product treatment.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carried into practice.

In the drawing:

FIGS. 1 to 4 are highly schematic portrayals of the different locations of metallurgical products on a kiln hearth in the course of a unit cycle of advance of all the products.

On a kiln hearth 1, formed of an upper heat accumulating and conducting layer 2 and a lower insulating layer 3, are placed, at regular intervals shown by one of the dimensions 4, identical products 5 having a width represented by the dimension 6.

The hearth areas 7 between the products 5 receive from the kiln arch a radiation represented'by an arrow 8, and the upper surfaces of the product 5 receive the same radiation indicated by an arrow 9.

Considering a specific product 5a shown in hatched lines and the uncovered hearth area 7a which appears upstream with respect to the direction of advance, then if all the products 5 are shifted in an elemental movement of amplitude equal to dimension 4, it will be seen that product 5a will cover up an area 7b which lay downstream prior to said movement and which had accumulated heat while it was exposed to the arch radiation, thus enabling it, when it is covered, to restore this heat to the facing surface of product 5a; at the same time, the upstream product 50 covers up the area 70 which accordingly restores to the undersurface of product 5c the heat it had previously stored. These processes of giving up heat are indicated by the small arrows 10.

If, as shown in FIG. 3, the entire set of products is caused to describe an elemental backward movement which fetches the products back into the position of FIG. I, then another portion of the width of product 5a will cover up the hearth area 7c which had received heat during the previous phase of immobility of the products. Thus, after their time of dwell in this position, the products will have received heat along both edges of their undersurfaces.

As shown in FIG. 4, the third elemental movement is finally imparted to the product with an amplitude twice the value of the previous elemental movements, but in the downstream direction. Thus product 5a exposes a middle portion to the hearth area 7d which had remained uncovered during the previous phase of dwell.

As a result, in the course of a complete cycle of forward travel, the undersurface of a product 5a has recovered heat from the hearth by contact with areas thereof successively exposed to the arch radiation and subsequently covered up by fractional areas of said undersurface.

By way of example, the upper layer 2 could be fonned of bricks or a chromium bearing refractory cement, while the bottom layer could be made of any conventional insulating material.

In the particular example herein described, the thickness of the treated product is equal to about one-third of its width, which explains why the elemental movements are respectively equal to one-third of the width of the product in the case of the first two movements, and to two-thirds thereof in the case of the third movement. Manifestly, other fractional values could be adopted, such values being preferably chosen so as to achieve a juxtaposition, beneath the undersurface of the products, of the contact areas with the previously uncovered counterpart areas on the hearth, whereby to obtain a uniform heating by heat recovery.

It should be noted that such recovery-heating is not easy to accomplish it the process of forward travel of the products is not made up of elemental movements involving a phase of alternating directions of travel, for the following reasons:

Considering first a forward travel consisting of elemental movements in the same direction, without heat recovery, the times of dwell of the products between two consecutive advances would have to be lengthened, and since the increase in the dwelling time would not be proportional to the increase in thickness, there would be a marked reduction in output from the kiln.

Considering on the other hand forward motions which will permit of a degree of heat recovery through the use of a pitch equal to the width of the product involved, then although the total dwelling time can obviously be reduced, on the other hand less hearth area is occupied and production is once more too low. Further, the recovery of heat from the hearth takes place only during the first moments which follow the depositing of the product on the hot hearth, so that a long dwelling time prevents the advantage conferred by heating off the hearth from being fully exploited.

Consequently the method hereinbefore described allows of reducing the dwelling time in the kiln and recovering maximum heat from the hearth with optimum efliciency (short dwelling times between consecutive elemental movements composing the cycle of forward travel), while at the same time providing the necessary dwelling times for the products in the kiln through the adoption of elemental movements in altemating directions and an acceptable charging percentage in relation to the hearth area. In such cases, the rate of output of the products herein considered, from the kiln, reaches its maximum.

it goes without saying that changes could be made in the method described hereinabove without departing from the scope of the invention. By way of example, other fractional values of the width of the face of a product in contact with the hearth of the kiln could be adopted, while the various equal or unequal elemental movements could be carried out in any other What I claim is:

1. In a method of heating in a furnace or kiln products such as mutually spaced metallurgical products conveyed onto the hearth of said furnace or kiln, the heating being performed by radiation reaching at least the upper surfaces of said products and the uncovered hearth areas in the spaces between the products, the combination comprising the steps of; imparting to said products collectively successive unit advancing motions, each of said motions comprising basic reciprocating movements, the extents of said movements being of values equal to or in multiples of fractions of the width of the face of each of said products in contact with said hearth, each said fraction being essentially equal to said mutual spacing, and arresting said motion for periods constituting dwelling times of predetermined equal durations subsequent to each of said basic movements.

2. A method according to claim 1, wherein at least one said basic movement is of a magnitude greater than that of the others.

3. A method according to claim 1, wherein at least one basic movement is of a magnitude less than that of the others. 

1. In a method of heating in a furnace or kiln products such as mutually spaced metallurgical products conveyed onto the hearth of said furnace or kiln, the heating being performeD by radiation reaching at least the upper surfaces of said products and the uncovered hearth areas in the spaces between the products, the combination comprising the steps of; imparting to said products collectively successive unit advancing motions, each of said motions comprising basic reciprocating movements, the extents of said movements being of values equal to or in multiples of fractions of the width of the face of each of said products in contact with said hearth, each said fraction being essentially equal to said mutual spacing, and arresting said motion for periods constituting dwelling times of predetermined equal durations subsequent to each of said basic movements.
 2. A method according to claim 1, wherein at least one said basic movement is of a magnitude greater than that of the others.
 3. A method according to claim 1, wherein at least one basic movement is of a magnitude less than that of the others. 